1. Technical Field
The present invention relates to a piezoelectric element, a liquid ejecting head, and a liquid ejecting apparatus and particularly relates to a piezoelectric element, a liquid ejecting head, and a liquid ejecting apparatus that are free from electrification-induced dielectric breakdowns of the piezoelectric body contained therein.
2. Related Art
Piezoelectric elements are stretched or contracted on application of voltage, and their use includes the source of driving force for diaphragms and actuators for liquid ejecting heads (ink jet heads).
Piezoelectric elements for liquid ejecting heads, which require fine patterning, are made of a ferroelectric piezoelectric material, such as PZT (lead zirconate titanate). However, ink, water (moisture), and other external factors often degrade the pressure capacity and other properties of PZT. As a solution to this problem, JP-A-2005-178293 has proposed covering a piezoelectric element with a protective layer. This protective layer is preferably made of a highly insulating, low-dielectric, and highly waterproof material. More preferably, this material has a low Young's modulus for greater displacements.
However, such a highly insulating protective layer usually has a high dielectric constant and thus is easily electrified. Also, even a less dielectric protective layer may still be electrified by surrounding static electricity. If electrified, the protective layer may cause a dielectric breakdown of the piezoelectric body adjacent thereto.